The present invention relates to a conference system which utilizes a time division digital switch.
Conventionally this kind of system employs a method which subjects participant's voices to an N-1 addition while holding their sound levels unchanged or after equally attenuating them for preventing singing. On this account, for example, in the case of a three-party communication involving a CO line A of a large line loss and intercom lines B and C of a small line loss, the intercom line B is supplied with the sum of voice (A) of the CO line A and voice (C) of the intercom line C, but the volume of the voice (A) is small and the volume of the voice (C) is large, so the voice of the CO line A is difficult to hear on the intercom line B.
Furthermore, when the participant's voices are equally attenuated for the prevention of singing, the voices that reach the participant of a large line loss are appreciably low and difficult to hear, and when a two-party communication is switched to a three-party one, sound volume variations are caused, creating a sense of incongruity.